Aaron's first team, with whom he signed while he was still in high school, was the semi-pro Birmingham Black Bears, but he was acquired in 1951 by the Negro American League champion Indianapolis Clowns after the Black Bears played an exhibition against the Clowns the previous year. The Clowns won the Negro League World Series in 1952 and Aaron's contract was acquired by the Braves, then still in Boston. After two years of excellent performance with the franchise's farm club affiliates, Aaron was brought up to the major league team (which had moved to Milwaukee before the 1953 season).

In his first season (1954) he was moved from shortstop to outfielder, and despite an injury which caused him to miss part of the season, posted a batting average of .280, which included thirteen home runs. The following year his average was .314, and in 1956 he was the NL batting champion with a .328 average and 26 home runs.

Aaron led the league in RBIs in 1957 with 132, 1960 with 126, and 1963 with 130. He and teammates Eddie Mathews and Warren Spahn led Milwaukee to pennants in 1957 and 1958 and defeated the New York Yankees in the 1957 World Series, after which Aaron was voted the league's Most Valuable Player for that year. By 1955 Aaron was being regularly selected as an outfielder for the National League's All-Star team.

He played most of his prime in Milwaukee's County Stadium, which was a poor home-run park. When the team moved to Atlanta in 1966, Aaron's home run output increased (Atlanta's Fulton County Stadium - famously friendly to hitters - was nicknamed "The Launching Pad"); he hit 44 homers his first season there. His hallmark was consistency: his best home run season was "only" 47 (in 1971), but he sustained high levels of production for over 20 years. This enabled him to approach the home run record in the early 1970s.

As a 39-year-old, Aaron hit exactly 40 home runs in 1973, ending the season with a career total of 713. Over the winter, Aaron endured death threats and a barrage of racist hate mail from people who did not want to see a black man break Ruth's home run record. However, when this harassment became widely known, the ballplayer enjoyed a massive flood of public support motivated at least partially to counter the bigotry. Near the beginning of the 1974 season, Hank Aaron broke the record on April 8, with a home run in Atlanta off Los Angeles pitcher Al Downing.

Although he is justifiably proud of his record for home runs, Aaron has numerous other baseball records including that for career total bases, a record he is particularly proud of because he feels it more accurately acknowledges his valuable contribution to his team.

Aaron now works as an executive with the Atlanta Braves organization. His autobiography I Had a Hammer was published in 1990.

Aaron now owns Hank Aaron BMW of south Atlanta where every car is sold with an autographed baseball.